Jellyfish have a complex life cycle: a single jellyfish reproduces both sexually and asexually during its lifetime, and takes on two different body forms. An adult jellyfish is called a medusa, which is the familiar umbrella-shaped form that we see in the water. Medusa jellyfish reproduce sexually by spawning—the mass release of eggs and sperm into the open ocean—with entire populations sometimes spawning all together. Male and female jellyfish (there aren't many hermaphrodites) release the sperm and eggs from their mouths. In most species, fertilization takes place in the water; in others, the sperm swim up into the female's mouth and fertilize the eggs within.